1. Field of the Invention
The present invention relates to cooking apparatuses. In particular, the present invention relates to a microwave oven capable of changing the way to supply microwaves into a heating chamber according to what is to be heated.
2. Description of the Background Art
Conventional microwave ovens have been known to have a magnetron to supply microwaves generated by the magnetron into a heating chamber containing a stuff to be heated and thereby heat the stuff.
An example of such microwave ovens is disclosed in Japanese Utility Model Laying-Open No. 56-115895, according to which the position of a radiation antenna is changed according to the shape of a stuff to be heated so as to change the position, in the direction of the height, where microwaves are concentrated, thereby preventing uneven heating.
Another example of such microwave ovens is disclosed in Japanese Patent Laying-Open No. 60-130094, according to which an antenna for supplying microwaves generated by a magnetron into a heating chamber is formed by bending a sheet metal and the antenna is rotated so as to avoid overheating of a central portion on the bottom of a heating chamber.
The above-described conventional microwave oven which changes only the height of the position where heating is concentratedly done, however, may or may not be able to satisfactorily address the multiplicity of the shape of a stuff to be heated.
Further, although it may be advantageous in some cases to avoid a central portion of the bottom of food from being concentratedly heated, the concentrated heating of the central portion may be appropriate in a particular case. In other words, the avoidance of the overheating of the central portion on the bottom of the heating chamber could be inappropriate depending on the type and shape of a stuff to be heated or depending on the state in which the stuff is placed in the heating chamber.
The present invention has been made in consideration of the above-described circumstances. An object of the present invention is to provide a microwave oven capable of changing the way to supply microwaves into a heating chamber according to what is to be heated.
A microwave oven according to the present invention includes a heating chamber holding food therein, a magnetron generating microwaves, a radiation antenna provided in the heating chamber for radiating the microwaves generated by the magnetron into the heating chamber, and an antenna moving unit moving the radiation antenna. The radiation antenna includes a first plane facing an inner wall of the heating chamber and a second plane facing the inner wall and located closer to the inner wall relative to the first plane. The first plane has an opening formed therein. The antenna moving unit is capable of moving the radiation antenna between a first position and a second position by changing the distance between the radiation antenna and the inner wall, the radiation antenna at the first position radiating the microwaves generated by the magnetron from an edge of the opening and the radiation antenna at the second position radiating the microwaves generated by the magnetron from respective edges of the first plane and the second plane.
According to the present invention, the distance between the radiation antenna and the inner wall can be changed by the antenna moving unit so as to change the impedance regarding microwaves in the space between the radiation antenna and the inner wall. Thus, by the antenna moving unit, the radiation antenna is allowed to supply microwaves from a part of the antenna into the heating chamber or to supply microwaves from the entire region of the antenna into the heating chamber.
In this way, the way to supply microwaves into the heating chamber of the microwave oven can be changed according to what is to be heated.
Preferably, regarding the microwave oven according to the present invention, the antenna moving unit rotates the radiation antenna.
Thus, when it is desired that the microwaves should be supplied into the whole of the heating chamber, microwaves can uniformly be supplied into the whole of the heating chamber.
Preferably, regarding the microwave oven according to the present invention, the antenna moving unit moves the radiation antenna between the first position and the second position while rotating the radiation antenna.
Thus, it rarely occurs that the radiation antenna is moved without being rotated, which reduces the cases in which users feel uneasy from the fact that no component is rotating.
Preferably, regarding the microwave oven according to the present invention, the antenna moving unit moves the radiation antenna in a predetermined manner before the magnetron starts generating microwaves.
Thus, generation of microwaves by the magnetron can be started after the radiation antenna is moved to an appropriate position. Accordingly, it can be avoided that microwaves are generated while the radiation antenna is placed at infinite number of positions between the first position and the second position and thus it can be avoided that an infinite number of electromagnetic-field-distribution patterns are present.
Preferably, regarding the microwave oven according to the present invention, the antenna moving unit stops the radiation antenna at a predetermined position when the magnetron completes its operation.
Thus, control for moving the radiation antenna is facilitated.
Preferably, the microwave oven according to the present invention further includes a switch turned on/off according to where the radiation antenna is positioned, the switch being turned off when the radiation antenna is at the predetermined position.
Thus, the period of time during which the switch is turned on can be shortened, which is advantageous for extension of the lifetime of the switch.
Preferably, regarding the microwave oven according to the present invention, the antenna moving unit stops the radiation antenna at the first position or the second position only.
Thus, control of the position of the radiation antenna by the antenna moving unit can be facilitated.
Preferably, the microwave oven according to the present invention further includes a number storing unit storing the number of times the radiation antenna has been stopped at the first position and the number of times the radiation antenna has been stopped at the second position. When the microwave oven is powered, the antenna moving unit stops the radiation antenna at one of the first position and the second position, at which the radiation antenna has been stopped a greater number of times which is stored in the storing unit.
Thus, the radiation antenna can efficiently be moved.
Preferably, the microwave oven according to the present invention further includes a number storing unit storing the number of times the radiation antenna has been stopped at the first position and the number of times the radiation antenna has been stopped at the second position. When the magnetron completes its operation, the antenna moving unit stops the radiation antenna at one of the first position and the second position, at which the radiation antenna has been stopped a greater number of times which is stored in the storing unit.
Thus, the radiation antenna can efficiently be moved.
Preferably, the microwave oven according to the present invention further includes an antenna position sensing unit detecting that the radiation antenna is at the first position and/or the second position. The antenna moving unit stops the radiation antenna from moving when no sensing output is obtained from the antenna position sensing unit even though the radiation antenna is moved for a predetermined time.
Thus, it can be avoided that certain operations for moving the radiation antenna are continued in spite of the fact that the radiation antenna is not normally moved.
Preferably, the microwave oven according to the present invention further includes a magnetron control unit controlling operation of the magnetron. The magnetron control unit stops the magnetron from generating microwaves when no sensing output is obtained from the antenna position sensing unit even though the antenna moving unit moves the radiation antenna for a predetermined time.
Thus, it can be avoided that certain operations for moving the radiation antenna are continued in spite of the fact that the radiation antenna is not normally moved.
Preferably, the microwave oven according to the present invention further includes a notifying unit providing a notification, when the antenna moving unit stops movement of the radiation antenna, that the antenna moving unit stops the radiation antenna from moving for the reason that no sensing output is obtained from the antenna position sensing unit.
Thus, a user can easily know the fact that the radiation antenna is not normally moved.
Preferably, the microwave oven according to the present invention further includes a magnetron control unit controlling operation of the magnetron. The magnetron control unit allows the magnetron to generate microwaves on the condition that the radiation antenna is stopped at the first position or the second position.
Thus, the way to supply microwaves into the heating chamber of the microwave oven is accurately controlled.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.